1. Field of the Invention
This invention relates to a developing apparatus for use in a copying machine, a printer, a facsimile apparatus or the like adopting an electrophotographic process or an electrostatic recording process.
2. Description of Related Art
In an image forming apparatus of this kind, there is well known a method of carrying a dry developer as a visualizing agent on the surface of a developer carrying member, conveying and supplying the developer to the vicinity of the surface of an image bearing member bearing an electrostatic latent image thereon, and developing and visualizing the electrostatic latent image while applying an alternating electric field to between the image bearing member and the developer carrying member. Generally a developing sleeve is often used as the developer carrying member and therefore, the developer carrying member will hereinafter be referred to as the “developing sleeve”, and generally a photosensitive drum is often used as the image bearing member and therefore, the image bearing member will hereinafter be referred to as the “photosensitive drum”.
As a developing method, there is known a so-called magnetic brush developing method of using, for example, a developer (two-component developer) comprising a two-component composition (carrier particles and toner particles), forming a magnetic brush on the surface of the developing sleeve having a magnet disposed therein, rubbing or bringing this magnetic brush against or close to the photosensitive drum opposed to the developing sleeve with a minute developing gap held therebetween, and continuously applying an alternating electric field to between the developing sleeve and the photosensitive drum (between S-D) to thereby respectively effect the shift and reverse shift of the toner particles from the developing sleeve side to the photosensitive drum side, thereby effecting development (see, for example, Document 1 (Japanese Patent Application Laid-Open No. S55-32060) and Document 2 (Japanese Patent Application Laid-Open No. S59-165082).
A developing apparatus for the above-described two-component magnetic brush developing is of a construction as shown in FIGS. 7 and 8 of the accompanying drawings. FIG. 7 is a cross-sectional view of a conventional developing apparatus, and FIG. 8 is a plan view thereof, and in FIGS. 7 and 8, the reference numeral 101 designates a developing sleeve, the reference numeral 102 denotes a magnet roller fixedly disposed in the developing sleeve 101, the reference numeral 103 designates a developing chamber screw, the reference numeral 104 denotes an agitating chamber screw, the reference numeral 105 designates a developing container, the reference character 105a denotes a toner supply port, the reference character 105b designates a developing chamber, the reference character 105c denotes an agitating chamber, the reference numeral 106 designates a regulating blade disposed to form a thin layer of developer on the surface of the developing sleeve 101, the reference numeral 107 denotes a toner storing container for storing a toner therein, and the reference numeral 108 designates a supplying screw for supplying the toner from the toner storing container 107 to the developing apparatus. As shown, the developing sleeve 101 is disposed in proximity to a photosensitive drum 109, and is rotated in an opposite direction to or the same direction as the direction of rotation of the photosensitive drum 109, and is set so that a developer (indicated by hatching) can develop in contact with the photosensitive drum 109.
A developer consisting of toner particles and a magnetic carrier mixed together is contained in the developing container 105, and the mixing ratio (hereinafter referred to as the T/C ratio) of the toner particles and the magnetic carrier is such that an amount of toner corresponding to the toner consumed by developing is supplied from the toner storing container 107 in which the toner to be supplied is contained by the supplying screw 108. The supplied developer drops and is supplied into the agitating chamber in which the agitating chamber screw 104 is provided, via the supply port 105a of the developing container 105, whereby the T/C ratio is kept constant. As methods of detecting and maintaining the mixing ratio of the toner particles and the magnetic carrier in the developing container 105 at this time, there have heretofore been proposed various methods.
For example, a method of providing detecting means around the photosensitive drum, applying light to the toner transferred from the developing sleeve side to the photosensitive drum side, adjusting the toner supply amount from transmitted light and reflected light at this time and maintaining the T/C ratio, a method of providing detecting means on the developing sleeve, and detecting the T/C ratio from reflected light when light is applied to the developer applied onto the developing sleeve, a method of providing a sensor in the developing container, and detecting any change in the apparent permeability μ of the developer in a constant volume near the sensor by the utilization of the inductance of a coil to thereby detect the T/C ratio (hereinafter referred to as the toner density detecting sensor), etc. have been proposed and put into practical use.
The toner density detecting sensor utilizing the change in the permeability of the developer is such that for example, when the permeability has become great, it means that the T/C ratio in the developer in a constant volume has become low, and this means that the amount of toner in the developer has decreased and therefore, toner supply is started. Conversely, when the permeability has become small, it means that the T/C ratio in the developer in the constant volume has become high, and this means that the amount of toner in the developer has increased and therefore, the T/C ratio is controlled on the basis of such a sequence as stops toner supply.
On the other hand, as shown in FIG. 8, the developing sleeve 102, the developing chamber screw 103 and the agitating chamber screw 104 are rotatively driven in predetermined directions at a predetermined speed by a drive source such as a motor not shown, via drive transmitting means such as a gear train, whereby the developer in the developing container 105 is circulated in the direction indicated by the arrow indicated in FIG. 8. Indicated by a grid line is the position of the toner supply port 105a. A fresh toner supplied through this supply port 105a is uniformly agitated with the developer while it is carried over the length A of the agitating chamber, and is sufficiently subjected to triboelectrification and is circulated to the developing chamber. In the developing chamber, the magnetic brush of the developer is formed by a developing magnetic field formed by the magnet roller which is also the shaft of the developing sleeve, and the toner adhering to the magnetic brush and the toner adhering to the surface of the developing sleeve 102 shift to the image area of an electrostatic latent image formed on the photosensitive drum 109 and developing is effected.
In recent years, however, with the spread of copying machines, printers, facsimile apparatuses, etc. using the electrophotographic process, the electrostatic recording process or the like, the demand from the market for the downsizing of those apparatuses and the larger capacity of the toner storing container for a reduction in running cost is very strong. FIGS. 9A and 9B of the accompanying drawings are views for illustrating a factor which determines the height of an image forming apparatus using the aforedescribed two-component developing apparatus, and FIG. 9A is a schematic cross-sectional view, and FIG. 9B is a schematic rear view taken along the direction indicated by the arrow V in FIG. 9A. Here, the height H1 of the developing apparatus in the image forming apparatus is determined by another element in the developing apparatus which is not shown, and it is assumed that the position H1 shown in FIG. 9A is the lowest position at which the developing apparatus can be disposed.
As already described, with the lowering of the T/C ratio in the developing apparatus, the toner is supplied from the toner storing container 107 through the supply port 105a via the supplying screw 108. Generally, a supply port and a shutter mechanism are provided at a position higher than the height of the surface of powder in the supply port. This is because the developing container is an interchangeable unit and therefore, if the supply port and the shutter are at a position higher than the surface of powder, it is difficult for the developer to scatter during the mounting and dismounting thereof.
Also, as regards the carrying of the toner, it is desirable to carry the toner from above to below or horizontally without opposing gravity as far as possible, and in order also to avoid such an inconvenience as the remaining or clogging of the toner in a toner carrying path, it is preferable to avoid the carrying of the toner from below to above. Accordingly, to avoid such inconveniences as the scattering of the developer and the remaining or clogging of the toner in the toner carrying path, it is desirable to provide the supply port at a position higher than the surface of powder in the developing container, and dispose the toner storing container and the supplying screw at the same position as or a position higher than that.
Here, from the viewpoint of the downsizing of the apparatus, the dimension to the uppermost surface (H2 in FIG. 9A) should be made as small as possible, and from the viewpoint of making the toner storing container large in capacity to reduce the running cost, the space higher than the surface of powder in the developing container (H2 dimension in FIG. 9A) should be made as large as possible and therefore, it will be seen that “the downsizing of the apparatus” and “the larger capacity of the toner storing container” are mutually contradictory requirements.
That is, if the conventional construction remains unchanged, to satisfy one of “the downsizing of the apparatus” and “the larger capacity of the toner storing container”, the other will be sacrificed, and to satisfy both, the supply port will be provided at a position lower than a powder surface or the toner storing container will be disposed at a position lower than the developing apparatus to thereby effect the carrying of the toner opposing gravity, and cause such inconveniences as the scattering of the developer and the remaining or clogging of the toner in the toner carrying path, thus spoiling the reliability as the developing apparatus. This has been the great problem that in the image forming apparatus, the downsizing of the apparatus and the larger capacity of the toner storing container and the maintenance of reliability cannot be satisfied at a time.